The invention is directed generally to automatic color correction circuits for use in color television receivers. The invention is specifically directed to an improved network for automatically enabling such a color correction circuit when broadcast color signals have a hue within a selected range of fleshtone hues, and for disabling the color correction circuit at other times.
Most modern color television receivers include color correction circuitry for automatically modifying the hues of reproduced color images in order to develop fleshtones whose hues are more consistent than those which are broadcast. Some color correction circuits alter the phase of 3.58 MH.sub.z color signals prior to their demodulation, and other such circuitry operates on demodulated color signals to provide hue correction. Irrespective of which approach is used, it is preferable to alter the hues of only those color signals which are representative of fleshtones, or those which are within a selected range of fleshtone hues. Color signals such as blues and greens which are far removed from fleshtones are preferably not modified.
For this purpose, it has been proposed to automatically enable the color correction circuit when color signals within a range of fleshtones are received, and to disable the color correction circuit at all other times. The problem which has arisen in the implementation of this approach is that it has been difficult to enable the color correction circuit only over a relatively precise range of color signals. The result has been that similar color television receivers have been unable to reliably and consistently produce similar color images.
Another factor which must be accounted for in the design of enabling networks for color correctors is the trend toward complete integration of the signal processing circuitry in television receivers. Hence, any such enabling network should be capable of construction in integrated circuit form, and should particularly not require the use of an excessive number of input/output pins for coupling the enabling network to discrete circuit components.